The fact is known that amine-containing hydrocarbon ligands present as solutes in a solvent such as water are characterized by their ability to selectivity form strong bonds with the transition metal ions or groups of these ions present as solutes in the same solvent as described in a book by R. M. Smith and A. E. Martell, CRITICAL STABILITY CONSTANTS VOL. 2: AMINES, Plenum Press, New York, 1975, pp. 1-401. However, researchers have not previously been able to effectively incorporate amine-containing hydrocarbon ligands into separation systems where the behavior of the amine-containing ligands in the separation systems in comparison to that of the amine-containing ligand as a solute is unchanged and/or the amine-containing ligand will remain in the separation system for repeated separations of cations. Articles such as those entitled SILANE COMPOUNDS FOR SILYLATING SURFACES by E. P. Plueddemann, in "Silanes, Surfaces and Interfaces Symposium, Snowmass, 1985," Ed. by D. E. Leyden, Gordon and Breach, Publishers, 1986, pp. 1-25 and SILANE COUPLING AGENTS by E. P. Plueddemann, Plenum Press, 1982, pp. 1-235 list many different types of organic materials which have been attached to silane compounds and discusses some of their properties. The preparation and uses of amine-containing hydrocarbons attached to silane or silica through a hydrocarbon linkage is discussed. The structures reported in those publications contained only aminopropyl and ethylene diaminopropyl groups (Formula 1 where a - 3, b=0, c-0 or 1, d=0, B=NH, D is not present, E-H or NH2 and R2 -H). These latter compounds were used to complex copper ions.
E. P. Plueddemann in METAL EXTRACTION FROM SOLUTION AND IMMOBILIZED CHELATING AGENTS USED THEREFORE. Canadian Patent No. 1,196,618 of Nov. 12. 1985 reported the preparation of a variety of amine-containing silica gel materials. These materials were made by first reacting chloropropyltrimethoxysilane with the amine forming a trimethoxysilane containing the amine function which was coated onto silica gel and heated to effect a covalent attachment of the amine to the silica gel. The resulting compound had the amine function three carbon atoms removed from silica. These materials do complex and thus remove heavy metals. However, these types of aminopropyl functions are not completely stable as discussed in the next paragraph. The Plueddemann Canadian patent lists other references concerning the same type of silica gel-bound amine complexing materials.
It is known fact that amine functional groups attached to silica gel, where the amine function is three carbon atoms removed from the silica gel, are not completely stable. E. P. Plueddemann, in the above mentioned article in the book edited by D. E. Leyden, reported that his amine materials (amine group three atoms removed from silane) slowly lost their ability to complex copper II. D. M. Wonnacott and E. V. Patton in HYDROLYTIC STABILITY OF AMINOPROPYL STATIONARY PHASES USED IN THE SIZE-EXCLUSION CHROMATOGRAPHY OF CATIONIC POLYMERS, Journal of Chromatography, vol. 389, pp. 103-113 (1987) and
/7 T. G. Waddell, D. E. Leyden and M. T. DeBello in THE NATURE OF ORGANOSILANE TO SILICA-SURFACE BONDING, Journal of Americal Chemical Society, vol. 103, pp. 5303-5307 (1981) discuss the stability of the aminopropyl-silica gel types of materials. In the conclusion to the Wonnacott and Patton article it is stated that "aminoalkyl silanes which have been used extensively in the synthesis of silica-based, weak ion exchangers do not lend themselves to this type of chromatography due to their hydrolytic instability."
Bonded silica gel phase supports containing amine functions have been prepared by reacting the amine with 3.glycidoxypropylsilane bonded to silica gel. S. H. Chang, K. M. Gooding and F. E. Regnier in USE OF OXIRANES IN THE PREPARATION OF BONDED PHASE SUPPORTS, Journal of Chromatography, vol. 120, pp. 321-333 (1976) and M. A Bagnoud, J. L Veuthey and W. Haerdi in INTERACTIONS SILICE METALLIQUE-SOLUTE: POSSIBILITE d'APPLICATIONS en PRECONCENTRATION et en CHROMAOGRAPHIE d'ECHANGE de LIGANDS (LEC), Chimica, vol. 40, pp. 432-434 (1986) have reacted amines with 3.glycidoxypropyl-bonded silica gel. Chang, Gooding and Regnier reported on four such compounds prepared from diethylamine [Formula 1, where a=3, b=1, c and d=0, R.sup.1 =OH, and E =N (ethyl)2], dimethylaminoethanol [FIG. 1, where a=3, b=1, c=1, d=0, B=0, R.sup.1 =OH, R.sup.2 =H, E - N (methyl).sub.2 ], diethylaminoethanol [same as the previous structure except N(ethyl)2 at the end], and polyethyleneamine [Formula 1, same as previous formula except c is a large number and E=NH.sub.2 ]. These materials were used to separate proteins but not metal cations. Bagnoud, Veuthey and Haerdi prepared a compound from a cyclic tetraamine (cyclam) which does not have a structure similar to the structures of FIG. 1. This material was used to bind metal ions and the bound metallic material was used in liquid exchange chromatography to separate certain organic compounds. In neither of these studies were metal ions separated and recovered.
There is a particular need in modern society to (1) measure the concentrations of heavy metal cations in the low part per billion (PPB) concentration; (2) to remove low levels of toxic heavy metal ions from solutions such as potable water; and (3) to recover valuable metal ions Present in solution at low levels. For example the allowable amounts of lead, mercury, cadmium and silver ions in drinking water are in the low PPB levels. Present methods for analysis of these cations are not accurate at those levels without time consuming methods to concentrate the cations up to the low part per million level. Furthermore, removal of the metals is not selective, but is expensive and equipment intensive using present methods. Thus, the complexing properties of hydrolytically stable amine-containing hydrocarbon ligands attached to an inorganic support such as silica gel or titanized silica gel are of the utmost importance for the repeated separation and concentration of certain heavy metal cations for analysis, and/or recovery purposes. The process of the present invention using the amine-containing materials of Formula 1 accomplish this feat.